Electrochemistry
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Electricity
Movt of electrons
 Movt of electrons through wire connecting
2 half-reactions  electrochemical cell
 Also called voltaic or galvanic cell
 Cell produces current from spont rxn
 Ex: copper in soln of AgNO3 is spont
 Electrolytic cell uses electrical current to
drive a non-spont chemical rxn
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Voltaic cell
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Solid Zn in zinc ion soln = half-
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Likewise, Cu/Cu ion soln
Wire attached to each solid
Salt bridge =
1. contains electrolytes,
2. connects 2 half-cells,
3. anions flow to neutralize
accumulated cations at anode
and vice-versa (completes
circuit)
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cell
“An Ox” = anode
oxidation
 Has negative charge
cuz releases e “Red Cat” =
reduction cathode
 Has positive charge
cuz takes up e
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Electrical current
Measured in amperes (A)
1 A = 6.242 x 1018 e-/s
Electric current driven by diff in potential E/unit
of charge
 Pot diff (electromotive force or emf) = volt (V)
 1 V = J/C
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Batteries
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Dry-cell batteries
Don’t contain large amts of water
Duracell
Anode: Zn oxidized
Cathode: 2MnO2(s) + 2NH4+(aq) + 2e-  Mn2O3(s)
+ 2NH3(g) + H2O(l)
Cathode is Carbon-rod immersed in moist
(acidic) paste of MnO2 that houses NH4Cl
1.5 V
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Batteries
More common dry-cell type: alkaline
battery
 Anode: Zn(s) + 2OH-(aq)  Zn(OH)2(s) + 2e Cathode:
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2MnO2(s) + 2H2O(l) + 2e- 2MnO(OH)(s) + 2OH-(aq)
Longer shelf-life, “live” longer
 Cathode in basic paste
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Batteries
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Lead-acid storage batteries
In cars
6 electrochemical cells (2V) in series
Anode: Pb(s) + HSO4-(aq)  PbSO4(s) + H+(aq) + 2eCathode:
PbO2(s) + HSO4-(aq) + 3H+(aq) + 2e-  PbSO4(s) + 2H2O(l)
In 30% soln of sulfuric acid
If dead, due to excess PbSO4 covering electrode surfaces
Re-charge (reverse rxn)  converts PbSO4 to Pb and
PbO2
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Rechargeable batteries
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Ni-Cd
Anode: Cd(s) + 2OH-(aq)  Cd(OH)2(s) + 2eCathode:
2NiO(OH)(s) + 2H2O(l) + 2e-  2Ni(OH)2(s) + 2OH-(aq)
KOH, usually, used
1.30 V
Reverse rxn recharges battery
Excess recharging  electrolysis of water
EXPLOSION!!!
Muhahahaha!
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Rechargeable batteries
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Cd toxic
Ni-MH
Hybrid car batteries: high energy density
Same cathode rxn
Anode: MH(s) + OH-(aq)  M(s) + H2O(l) + eCommonly, M = AB5, where A is rare earth
mixture of La, Ce, Nd, Pr, and B is Ni, Co, Mn,
and/or Mn
Very few use AB2, where A = Ti and/or V
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Rechargeable batteries
Anode made of graphite w/incorporated
Li-ions btwn carbon layers
 Ions spontaneously migrate to cathode
 Cathode = LiCoO2 or LiMn2O4
 Transition metal reduced
 Used in laptop computers, cell phones,
digital cameras
 Light weight and high E density
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Fuel cell
Reactants flow through battery
 Undergo redox rxn
 Generate electricity
 Hydrogen-oxygen fuel cell
 Anode: 2H2(g) + 4OH-(aq)  4H2O(l) + 4e Cathode: O2(g) + 2H2O(l) + 4e-  4OH-(aq)
 Used in space-shuttle program
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Electrolysis
Electrical current used
to drive nonspont
redox rxn
 In electrolytic cell
 Electrolysis of water
 Metal plating: silver
coated on metal,
jewelry, etc.
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